As raw material and waste disposal costs for glass fiber production escalate and environmental concerns regarding waste disposal increase, recycling waste glass fibers provides a cost effective means to decrease such costs and alleviate associated environmental concerns.
In the fiber glass industry, waste glass fibers can be produced in the fiber forming process and in subsequent processing operations, such as in the formation of yarns, fabrics, roving, chopped reinforcement and mat products. Various approaches have been used to process and recycle such waste glass fibers.
U.S. Pat. No. 5,352,258 discloses a process and apparatus which shred scrap glass fibers, dry the shredded glass fibers, remove contaminants such as metallic materials, and feed the shredded glass fibers to a glass melter. The feeder is preferably an auger feeder having a dead space at the end of the auger adjacent the melter. The dead space permits build up of shredded glass fiber material to insulate the metal auger from the heat of the melter, as discussed at column 11, lines 31-35 of the patent. The dead space has a length of around 1 to 12 inches along the longitudinal axis of the auger and before the interior of the melter, as discussed at column 13, lines 5-11.
U.S. Pat. No. 4,145,202 discloses a method for processing waste glass strands which includes the steps of cutting and draining free water from the glass strands, removing metal from the strands, drying and incinerating the strands, sieving the strands and, if the particles are too large, grinding or milling the strands to 60 to 325 mesh range.
U.S. Pat. No. 5,312,052 discloses an apparatus and method for reclaiming fiber reinforcement from cured sheet molding compounded (SMC) waste products including a roller mill assembly in which respective rollers of each roller pair are spaced apart and driven at different speeds. Each of the rollers have identical diameters and has serrations extending across the length of the roller. Each of the serrations has a cross-sectional shape in the form of a pointed tooth, as discussed at column 4, lines 4-9.
Typical grinding and milling operations are energy-intensive, have high maintenance costs and therefore are not economically desirable to include in a recycling process. Also, it is often difficult to pneumatically convey recycled glass fibers. There is a need for a system and process for recycling glass fibers which requires minimal energy input, is efficient, durable, inexpensive, and provides glass fiber material which is conveyable by pneumatic transport, compatible with the glass melt and can be sold as a product to be used to reinforce composites.